1. Field of the Invention
2. Description of the Related Art
Inkjet printers utilize print cartridges that provide a supply of ink for the printhead. The ink is drawn from the cartridge during printing and when depleted, the cartridge must be replaced. Often, the user of the printer is automatically advised when the ink cartridge is low on ink. Determining when an inkjet cartridge is out of ink can be a difficult undertaking. Because of the physics of the pressure regulation system, the inkjet printhead is not capable of delivering all of the ink stored in the cartridge. Therefore, there is no true out of ink condition. Rather, the condition that leads to the end of life for an inkjet printhead occurs when the fluid pressure of the cartridge can no longer be regulated at a level that allows the necessary ink flow. When the ink remaining in the pressure regulation system reaches a certain level, the pressure becomes too high to deliver ink at the expected jetting rate. Adding to the confusion over out of an ink condition is the fact that when the pressure regulation system begins to fail, initially only print images that require high flow rates will be affected by a degraded print quality. As additional ink is used, the pressure regulation system will continue to fail at lower ink flow rates until the print is degraded to the point at which the print quality is unacceptable to all users.
This same end of life phenomenon is exhibited regardless of whether the printhead is integrated into the ink cartridge or is a separate device. In systems in which the printhead is permanently (or semi-permanently) attached to the printer instead of to the cartridge, additional situations may be presented in which ink starvation can occur. In narrow flow systems, there is a requirement for the fluid system of the printhead to be primed incrementally during the printhead life. If the printhead becomes deprimed, then the starvation phenomenon will even occur during printing. In wide flow systems, it is generally not possible to prime the printhead in the printer. However, even in wide flow systems the printhead may become deprimed, which requires replacement of the printhead.
In addition to the foregoing problems, there is also the possibility that the fluid path of a permanent or semi-permanent printhead may become blocked. If the purge/prime system in the printer is not able to clear the blockage, then the printhead requires replacement. This is an expensive operation for either the customer or the manufacturer, depending on whether the printhead is still under warranty. Therefore, there is a need to determine if the printhead has a permanent fluid blockage. Unfortunately, there is no practical method used today to determine when the pressure regulation system of an inkjet printer begins to fail. What is needed is a technology that can determine when this system failure begins.
In view of the foregoing, users of inkjet printers are often confused as to whether an ink cartridge is out of ink. Frequently, ink cartridges are replaced when the ink is low, even though there is sufficient ink to continue printing, albeit at a lower print setting. However, absent this option, the efficiency of ink usage of many cartridges is underutilized. Ink cartridges used in thermal inkjet printers can become inoperable for many reasons, many of which cannot be diagnosed, and thus the cartridge is simply discarded. Ink cartridges can fail due to being clogged, deprimed or simply low on ink. In other instances, users can become frustrated after replacing an ink cartridge with a new cartridge and find the new cartridge also fails to work. In many instances, the user has failed to remove the protective tape before installing the new cartridge in the printer.
U.S. Pat. No. 5,315,316 discloses a method of detecting ink flow through a printhead. This patent requires that the initial temperature of the printhead be close to room temperature at the beginning of the test. After the printhead has completed a print job, there could be a significant amount of time needed in order for the temperature of the printhead to return to room temperature. There is no suggestion in this patent of any technique for determining if the printhead is deprimed or clogged.
U.S. Pat. No. 5,699,090 discloses an out of ink detector for a thermal inkjet printer. The technique for detecting an out of ink condition is based on setting the initial temperature of a printhead to a setting that is much higher than the printhead would reach in any jetting operation. Then, during a printing operation the temperature is measured. If the temperature remains high, then the cartridge is out of ink. If the temperature decreases, then there is ink remaining in the cartridge. Currently available inkjet printheads operate at printing temperatures approaching 70° C. Therefore, to set a temperature higher than 70° C. and to take into account variations, the temperature setting could approach about 100° C. A temperature of this magnitude could create permanent damage to the printhead.
U.S. Pat. No. 6,196,651 describes a method and apparatus for detecting the end of life of a print cartridge used in a thermal inkjet printer. The method disclosed detects an out of ink condition based on setting the initial temperature of the printhead to a predefined setting, then performing a print operation for a time period, then waiting a time period, and then measuring the temperature. If the temperature measured after the time period is greater than the initial temperature, then the cartridge is considered out of ink.
From the foregoing, it can be seen that a need exists for a technique to determine more accurately the nature of ink cartridge problems so that measures can be carried out, if possible, to remedy the same. Another need exists for an automatic assessment by the printer of specific cartridge problems so that if repairable, fewer otherwise usable ink cartridges will not be unnecessarily discarded. Yet another need exists for a technique to determine when the ink in a cartridge is low, so that even if the ink flow rate will not support a high print setting, a lower print setting can be used in order to utilize the remaining ink until depleted. Other needs exist for inkjet printers that can determine when the ink cartridges are clogged, whether depriming of the cartridge has occurred, and whether other nonfunctional states of the printhead exist.